The present invention generally relates to a system for controlling gain when time-sharing a tuner in a frequency diversity receiver. Two radio-frequency automatic gain control (RFAGC) filter capacitors are used, each capacitor corresponding to one of the currently utilized frequencies in the frequency diversity scheme. The capacitors are switched in tandem with the tuner frequency selection. This allows the capacitor associated with a tuned frequency to retain the RFAGC voltage until the tuner returns to that frequency.
This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Over-the-air television broadcasts have been gradually transitioning from analog to digital standards. In the United States, television transmissions have transitioned from the analog NTSC system to the digital ATSC system.
While ATSC signals can be reliably received at many fixed locations, reception by mobile receivers is highly problematic. Various extensions and modifications to the ATSC standard have been proposed to allow reliable reception at mobile receivers. Most provide backwards compatibility with ATSC, but employ various modulation, transmission, encoding, and redundancy techniques to assist mobile reception.
One such technique is the use of frequency diversity. With frequency diversity, the same information may be transmitted using signals on multiple carrier frequencies, such that when the information cannot be recovered from one of the signals, it might be recovered from the other. Frequency diversity provides improved immunity to multipath, which is a key factor in mobile reception difficulties. Reception can still be possible even if one of the frequency channels is unusable because of severe multipath impairment.
A common approach for reception in a frequency diversity system is to use two separate tuners and demodulator front-ends. This approach, however, can be cost-prohibitive. Sharing a single tuner and front-end could save money and reduce the physical size of the receiver electronics, but may create performance problems since there may not be enough time for robust signal acquisition each time the received channel frequency is changed. In particular, the time required to establish a radio-frequency automatic gain control (RFAGC) level may exceed the time available. A frequency diversity reception system is needed that provides the cost advantages of a single tuner system, but mitigates the performance issues related to signal acquisition. The invention described herein addresses this and/or other problems.